1. Field of Invention
This invention relates to polymer films. More particularly, this invention relates to ultrathin, cellulose ester polymer films and their production.
2. Prior Art
The preparation of films from cellulosic polymers on a liquid support, such as water, is known. For example, in U.S. Pat. No. 2,760,233, a process for preparing curved cellulose ester sheets is disclosed. However, no specific solvent mixtures and ratios suitable for casting ultrathin, pinhole-free, cellulose ester films are disclosed not are any film thickness given.
U.S. Pat. No. 3,445,321 discloses a process for producing hole-free, permselective films with thickness between 0.25 and 10 mils. Films are cast on a liquid surface, such as mercury. Suitable polymeric materials from which films can be prepared include cellulosic esters. However, the films of this patent are not ultrathin.
In U.S. Pat. No. 3,933,561, a process for preparing polymeric films on water is disclosed. The film thicknesses are usually less than about 2.5 microns (i.e., 25,000 angstroms) and thickness of 0.1 micron (i.e., 1,000 angstroms) are reportedly achieved. Polysaccharides, including cellulosic polymers, are reportedly suitable for the patent's process. However, specific solvent mixtures and ratios suitable for casting ultrathin, pinhole-free, cellulose ester films having thicknesses of 400 angstroms or less are not disclosed.
U.S. Pat. No. 3,551,244 discloses a process for preparing on a water surface films having thicknesses between 0.05 and 5.0 microns (i.e. between 500 and 50,000 angstroms). The patent lists polyssacharide derivatives, such as cellulose acetate, as suitable polymers. However, specific solvent mixtures and ratios suitable for casting ultrathin, pinhole-free, cellulose ester films having thickness of 400 angstroms or less are not disclosed.
U.S. Pat. Nos. 4,155,793, 4,272,855 and 4,374,891 disclose processes for preparing substantially void-free, ultrathin, permeable polymeric membranes having thicknesses of 500 angstroms or less. The patents assert that organic and inorganic polymers are suitable for use therein. However, only films prepared from organopolysiloxane-polycarbonate interpolymers mixed with polyphenylene oxide are disclosed in the examples. Cellulose ester films are not disclosed nor are suitable solvent mixtures and ratios for casting ultrathin, pinhole-free, cellulose ester films disclosed.
U.S. Pat. No. 2,689,187 discloses ultrathin nitrocellulose films. However, it does not disclose any organic cellulose ester films or suitable solvent ratios and mixtures for casting pinhole-free, ultrathin, cellulose ester films.
Other patents, such as U.S. Pat. Nos. 2,631,334, and 4,393,113, also disclose ultrathin polymeric films. However, no cellulose ester films are disclosed.
In the prior art, the preparation of ultrathin, pinhole-free, cellulose ester, free-standing films with thicknesses of less than 400 angstroms generally has not been disclosed. Usually, such polymer films with thicknesses of less than 400 angstroms that are cast contain holes or other macroscopic defects.
Therefore, it is an object of this invention to prepare ultrathin, cellulose ester polymer films.
It is a further object of this invention to prepare pinhole-free, cellulose ester polymeric films.
It is also an object of this invention to prepare free-standing, cellulose ester films having thicknesses of 400 angstroms or less.
These and other objects are obtained by the products and process of the present invention.